West Nile virus  


West Nile virus develops into a serious condition in less than 1 in 100 people who are infected 

How common is West Nile virus?

In the UK, no cases of WNV have been reported in people who have not travelled abroad.

Since 2002, when reporting for WNV began in the UK, there have been two reported cases (one in 2006 and one in 2007). Both cases involved people who had visited Canada.

2012 has been a particularly bad year for West Nile virus in America. There have been 5,387 cases reported, including 243 deaths, the highest figures in nine years. A third of all reported cases came from Texas.

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West Nile virus (WNV) is a virus spread by mosquitoes.

It is part of the flaviviridae family of viruses which also includes:

Most cases of WNV are not serious and many people have no symptoms or mild flu-like symptoms, such as muscle aches and a fever.

Serious symptoms occur in less than 1 in 100 people infected with the virus and include inflammation of the:

  • brain (encephalitis)
  • spinal cord
  • tissues surrounding the brain and spinal cord (meningitis)

Read more about the general and severe symptoms of West Nile virus.

How is West Nile virus spread?

WNV is usually spread through bites of infected mosquitoes. Mosquitoes become infected when they feed on infected birds. They can then spread the virus to humans and other animals they bite. 

In rare cases, WNV can be spread through an organ transplant or blood transfusion. The virus can also be passed from a mother to her baby during pregnancy or through breast milk, although this is also rare.

WNV is found in: 

  • Africa, including Egypt
  • Asia 
  • Australia
  • the Middle East, including Israel
  • some parts of Europe
  • the USA, including North, Central and South America 
  • some parts of Canada

Read more about the causes of West Nile virus.

Treating West Nile virus

There is no specific treatment for WNV. If your symptoms are mild, they will usually get better without treatment after a few days or weeks.

If your symptoms are more severe, you will need to go to hospital. You may be admitted and given supportive treatments, such as intravenous fluids (given through a drip in your arm), help with breathing and nursing care.

WNV can be fatal if it becomes severe. It is estimated that around 3-15 people in every 100 die. It is more likely to be fatal in elderly people.

Read more about treating West Nile virus and how West Nile virus is diagnosed.

Preventing West Nile virus

As there is no specific treatment for WNV, it's best to protect yourself from being bitten by mosquitoes when visiting affected areas. The mosquitoes that carry WNV are most active around dusk and dawn.

To avoid being bitten by mosquitoes you should:

  • wear loose-fitting, long-sleeved tops and long trousers to cover your skin as much as possible
  • use an insect repellent on exposed skin, taking care to avoid your eyes; DEET-based insect repellents are thought most effective
  • be aware mosquitoes can bite through thin clothing, so spraying clothes with insect repellent can help
  • use insect-proof screens on windows and doors and mosquito nets over the bed; air conditioning, mosquito plugs and spraying insecticide in the room may also help
  • avoid areas where there are likely to be large numbers of mosquitoes, such as near water

Read more about preventing WNV.

Page last reviewed: 14/11/2012

Next review due: 14/11/2014


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